A work machine such as, for example, an off-highway truck, may be large and heavy, making it difficult to decelerate. For example, an off-highway truck, such as the 797 produced by Caterpillar Inc. has a gross machine operating weight in excess of 687 tons. When operating a work machine this heavy, it is important to control its speed, especially when the work machine is traveling down an incline.
In order to maintain proper speed control over such a large and heavy work machine, the work machine may be outfitted with a retarding system that implements engine retarding and automatic transmission control. One such system is described in U.S. Pat. No. 6,249,733 (the '733 patent) to Smith. The '733 patent teaches an engine control system for automatically controlling an engine retarder and providing signals to control a transmission on a vehicle. If engine speed exceeds a predetermined engine speed level, the engine retarder is actuated to begin engine braking. When the vehicle reaches an appropriate speed, the transmission is automatically downshifted, thereby providing additional braking.
Although the engine control system of the '733 patent may sufficiently control the travel speed of a vehicle, it may create less than optimum situtations for the operator of the vehicle. For example, there may be instances when engine braking is desired to slow the vehicle, but downshifting is undesirable. When a downshift is automatically implemented during these situations, it may be necessary for the operator to manually adjust or readjust operation of the vehicle to account for the undesired downshift. Continued adjusting or readjusting of vehicle operation could result in efficiency and production losses of the vehicle.
The disclosed retarding system is directed to overcoming one or more of the problems set forth above.